Guaranteed mortgage packaging, or GMP, has not performed as well in the wholesale channel as ABN AMRO Mortgage Group had hoped since the product was first introduced to mortgage brokers in January 2003, according to a top company official. ABN AMRO, one of the pioneers of a fixed-price package of mortgage settlement services, originated about $1.7 billion under the “OneFee” program through its wholesale arm Interfirst Wholesale Mortgage Funding from January 2003 through August…